1. Field of the Invention
This invention relates to a table equipment having a table which moves in a line inclined to the horizontal plane.
2. Description of the Related Art
Generally, the table equipment used in machine tools or other machines has a table which moves along a horizontal plane.
A type of table equipment having a table which can move in the vertical direction is required for some machining methods.
When a table is moved in the vertical direction, the driving force to move the table varies with its moving direction since the table is subjected to the effect of gravitational acceleration. More specifically, to raise the movable table, a driving force which is the frictional force plus its gravity is required. To lower the movable table, a driving force which is the frictional force less its gravity is required.
Hence, the table equipment requires a motor which outputs force great enough to raise the table. The greater the output force of a motor, the larger the motor, and the more expensive the motor. The table equipment must inevitably be relatively large as a whole and comparatively expensive. A motor which generates a large driving force has a large inertia during its operation and has a poor response to operation signals. Therefore, it is impossible to position the movable table at high speed.
Further, it is difficult to precisely control the operation of the driving motor since the load on the motor varies in the rising and lowering of the movable table. To take an example, when a DC servo motor is used as a driving motor, it is necessary to change the gain of the control loop in the control device such as a servo amplifier according to the moving direction of the movable table. Control such as this is extremely difficult when moving the movable table at high speed and position it in short cycles.
Table equipment which solves the above problem is disclosed in Japanese Patent Laid-Open Nos. 62-68207, 62-68208, 62-68209 62-68210, all filed by the assignee of the present application. In each of them, a movable table is connected with a counterweight equal to the total weight thereof in such a way that the counterweight can move vertically, thereby eliminating the effect of the gravity acting on the movable table. This makes it possible to position the movable table accurately at high speed and in short-time cycles.
In any of the above inventions, however, the equipment is large in overall size because the weight of the counterweight needs to be equal to that of the movable table and the members fixed thereon.